Littoral cone

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A littoral cone lies on the right, on top of the cliffs

Littoral cones are a form of volcanic cone. They form from the interaction between lava flows and water. Steam explosions fragment the lava and the fragments can pile up and form a cone. Such cones usually form on ʻaʻā lava flows, and typically are formed only by large lava flows. They have been found on Hawaii and elsewhere.

Description

Littoral cones are semicircular cones which are breached in the direction of the lava flow that created them. They are formed by mounds of clasts that appear like cones without a crater.[1] Littoral cones are constructed by volcanic ash, lava bombs and lapilli.[2] Their component material is usually poorly sorted and can feature agglutinated structures and layering.[3] Sometimes spatter-fed lava flows occur on such cones.[4] They are formed by degassed hyaloclastite.[5][1] The most common form found on Hawaiʻi involves two semicircles on both sides of the lava flow that generated them;[6] some such cones in Hawaiʻi form a complete rim with diameters of 200–400 metres (660–1,310 ft).[7] Puʻu Kī in Hawaiʻi has nested craters on top of a lava tube.[8] Typically such cones are not larger than 800 metres (2,600 ft) wide and 75 metres (246 ft) high.[3] Other smaller cones in Hawaii have diameters of 40 metres (130 ft) and heights reaching 15 metres (49 ft).[9] They are not as well known as the Icelandic pseudocraters.[10]

Littoral cones not primary volcanic vents and distinguishing between a littoral cone and a primary vent can be difficult.[3] A littoral cone forms when lava flows from land into water. Interaction between the water and the lava leads to steam explosions. These explosions throw lava fragments into the air; under favourable circumstances these fragments pile up on land and form a cone.[11] This activity may resemble that of fire fountaining,[9] and produces tephra columns, lava bubbles, steam blasts and lava fountains.[12] Repeated phases of magma-water mixing lead to the formation of bedded deposits.[2] The steam explosions can lead to the formation of Pele's hair.[13] There are two types of such cones, depending on whether the magma-water mixing was free or whether it occurred in an enclosed environment; the former produces typical phreatomagmatic deposits, the latter more ash-poor cones than the former.[10]

The forming lava flows need to be sufficiently large;[14] the minimum size of lava flows that have formed such cones in Hawaiʻi is 38,000,000 cubic metres (50,000,000 cu yd).[15] Of these, about 5-6% of their volume is converted to fragments.[3] Usually littoral cones are formed by ʻaʻā lava as their fragmented nature allows ideal water-lava interactions, but pāhoehoe and intermediary lavas can also form littoral cones.[16] Other properties such as the speed of the lava flow and the structure of the flow front also influence the formation of littoral cones.[15] Larger lava flow rates generate larger cones.[17] In some littoral cones in Hawaiʻi that were formed by pāhoehoe lava flows, the collapse of a lava bench and subsequent steam explosions formed the cones instead.[7] Pyroclastic flows can also form littoral cones, one such cone has been found on Lombok and formed during the 1257 Samalas eruption.[18]

Examples

Pseudocraters and littoral cones have been found on Iceland, Hawaiʻi, Cerro Azul in the Galápagos Islands,[7] Deception Island, Antarctica,[19] and Medicine Lake Volcano, California.[20] Sometimes the words "pseudocrater" and "littoral cone" are used as synonyms.[21] Littoral cones are usually quickly removed by sea erosion; thus littoral cones rarely survive as landscape features.[11]

Prehistorical littoral cones have been found on the coast of Hawaiʻi, where the volcanoes Mauna Loa and Kīlauea face the sea. They were named "littoral cones" by Wentworth in 1938.[22] About 50 large cones are found on these two volcanoes and only three of them were formed during historical times; no such cones have been found on the other Hawaiian volcanoes.[11] The Puʻu ʻŌʻō and Mauna Ulu eruptions of Kīlauea have also formed small littoral cones.[7]

Examples of littoral cones include Sand Hills (1840 eruption) on Kīlauea in Hawaiʻi,[23] ʻAuʻau, Nā Puʻu a Pele, Puʻu Hou (1868 eruption) and Puʻu Kī (eruption 1300 years ago) at Mauna Loa in Hawaiʻi,[6] a cone close to Villamil at Sierra Negra, Galapagos,[24] several cones south of Krýsuvík[25] and Eldborg (1800 years ago) at Hengill both on Iceland,[26] a cone in the Winter Water unit of the Columbia Plateau Basalts, Oregon,[27] several cones along the shores of Lake Kivu in East Africa,[28] a cone at Becharof Lake, Alaska,[29] Burilan and Devil Rock on Gaua,[30] and Ponta de Ferraria (eruption 840 ± 60 years ago) on São Miguel Island, Azores.[31] The Speedwell Vent in Derbyshire, United Kingdom may also be a littoral cone of Carboniferous age.[32] Pleistocene littoral cones may also exist in Lake Tahoe, California,[33] while Archean littoral cones may have formed in the Barberton Greenstone Belt of South Africa.[34]

References

  1. ^ a b Fisher 1968, p. 839.
  2. ^ a b Richard V. Fisher; Hans-Ulrich Schmincke (6 December 2012). Pyroclastic Rocks. Springer Science & Business Media. pp. 263–264. ISBN 978-3-642-74864-6.
  3. ^ a b c d Green, Jack (1982-01-01). "Littoral cones". Beaches and Coastal Geology. Encyclopedia of Earth Science. Springer US. pp. 519–520. doi:10.1007/0-387-30843-1_260. ISBN 9780879332136.
  4. ^ Greeley, Ronald; Fagents, Sarah A. (25 September 2001). "Icelandic pseudocraters as analogs to some volcanic cones on Mars". Journal of Geophysical Research: Planets. 106 (E9): 20533. Bibcode:2001JGR...10620527G. doi:10.1029/2000JE001378.
  5. ^ Jurado-Chichay, Rowland & Walker 1996, p. 477.
  6. ^ a b Jurado-Chichay, Rowland & Walker 1996, p. 472.
  7. ^ a b c d Jurado-Chichay, Rowland & Walker 1996, p. 471.
  8. ^ Walker, George P. L. (1993). "Basaltic-volcano systems" (PDF). Geological Society, London, Special Publications. 76 (1): 25. Bibcode:1993GSLSP..76....3W. doi:10.1144/GSL.SP.1993.076.01.01. S2CID 128692790.
  9. ^ a b Jurado-Chichay, Rowland & Walker 1996, p. 478.
  10. ^ a b Holt, McPhie & Carey 2021, p. 2.
  11. ^ a b c Moore & Ault 1965, p. 3.
  12. ^ Holt, McPhie & Carey 2021, p. 3.
  13. ^ Mattox, Tari N; Mangan, Margaret T (January 1997). "Littoral hydrovolcanic explosions: a case study of lava–seawater interaction at Kilauea Volcano". Journal of Volcanology and Geothermal Research. 75 (1–2): 6–8. Bibcode:1997JVGR...75....1M. doi:10.1016/S0377-0273(96)00048-0.
  14. ^ Moore & Ault 1965, p. 9.
  15. ^ a b Moore & Ault 1965, p. 10.
  16. ^ Fisher 1968, p. 861.
  17. ^ Jurado-Chichay, Rowland & Walker 1996, p. 481.
  18. ^ Vidal, Céline M.; Komorowski, Jean-Christophe; Métrich, Nicole; Pratomo, Indyo; Kartadinata, Nugraha; Prambada, Oktory; Michel, Agnès; Carazzo, Guillaume; Lavigne, Franck; Rodysill, Jessica; Fontijn, Karen; Surono (8 August 2015). "Dynamics of the major plinian eruption of Samalas in 1257 A.D. (Lombok, Indonesia)". Bulletin of Volcanology. 77 (9): 7. Bibcode:2015BVol...77...73V. doi:10.1007/s00445-015-0960-9. S2CID 127929333.
  19. ^ Smellie, J.L. (27 April 2004). "Lithostratigraphy and volcanic evolution of Deception Island, South Shetland Islands". Antarctic Science. 13 (2): 201. doi:10.1017/S0954102001000281. S2CID 131008771.
  20. ^ "DIGITAL GEOLOGIC MAP DATABASE OF MEDICINE LAKE VOLCANO, CALIFORNIA". gsa.confex.com. Retrieved 2016-11-24.
  21. ^ EINARSSON, ARNI (February 1982). "The palaeolimnology of Lake Myvatn, northern Iceland: plant and animal microfossils in the sediment". Freshwater Biology. 12 (1): 65. Bibcode:1982FrBio..12...63E. doi:10.1111/j.1365-2427.1982.tb00603.x.
  22. ^ Fisher 1968, p. 842.
  23. ^ Fisher 1968, p. 841.
  24. ^ Reynolds, Robert W.; Geist, Dennis; Kurz, Mark D. (December 1995). "Physical volcanology and structural development of Sierra Negra volcano, Isabela Island, Gal´apagos archipelago". Geological Society of America Bulletin. 107 (12): 1401–1402. Bibcode:1995GSAB..107.1398R. doi:10.1130/0016-7606(1995)107<1398:PVASDO>2.3.CO;2.
  25. ^ Hersir, Gylfi Páll; Árnason, Knútur; Vilhjálmsson, Arnar Már; Saemundsson, Kristján; Ágústsdóttir, Þorbjörg; Friðleifsson, Guðmundur Ómar (27 November 2018). "Krýsuvík high temperature geothermal area in SW Iceland: Geological setting and 3D inversion of magnetotelluric (MT) resistivity data". Journal of Volcanology and Geothermal Research. 391: 6. doi:10.1016/j.jvolgeores.2018.11.021. ISSN 0377-0273. S2CID 135282804.
  26. ^ Stevenson, J. A.; Mitchell, N.; Mochrie, F.; Cassidy, M.; Pinkerton, H. (2009-12-01). "Lava entering water: the different behaviour of aa and pahoehoe at the Nesjahraun, Thingvellir, Iceland". AGU Fall Meeting Abstracts. 51: V51D–1749. Bibcode:2009AGUFM.V51D1749S.
  27. ^ "COLUMBIA RIVER BASALT AQUIFER CHARACTERISTICS REVEALED BY STATEMAP MAPPING IN OREGON'S UMATILLA BASIN". gsa.confex.com. Retrieved 2016-11-24.
  28. ^ Balagizi, Charles M.; Kies, Antoine; Kasereka, Marcellin M.; Tedesco, Dario; Yalire, Mathieu M.; McCausland, Wendy A. (1 August 2018). "Natural hazards in Goma and the surrounding villages, East African Rift System". Natural Hazards. 93 (1): 57. Bibcode:2018NatHa..93...31B. doi:10.1007/s11069-018-3288-x. ISSN 1573-0840. S2CID 134491982.
  29. ^ Lu, Zhong; Wicks, Charles; Dzurisin, Daniel; Power, John A.; Moran, Seth C.; Thatcher, Wayne (July 2002). "Magmatic inflation at a dormant stratovolcano: 1996-1998 activity at Mount Peulik volcano, Alaska, revealed by satellite radar interferometry". Journal of Geophysical Research: Solid Earth. 107 (B7): 4. Bibcode:2002JGRB..107.2134L. doi:10.1029/2001JB000471.
  30. ^ Métrich, N.; Bertagnini, A.; Garaebiti, E.; Vergniolle, S.; Bani, P.; Beaumais, A.; Neuville, D.R. (August 2016). "Magma transfer and degassing budget: Application to the 2009–2010 eruptive crisis of Mt Garet (Vanuatu arc)". Journal of Volcanology and Geothermal Research. 322: 49. Bibcode:2016JVGR..322...48M. doi:10.1016/j.jvolgeores.2015.06.003.
  31. ^ Lima, Ana; Nunes, João Carlos; Brilha, José (9 November 2016). "Monitoring of the Visitors Impact at "Ponta da Ferraria e Pico das Camarinhas" Geosite (São Miguel Island, Azores UNESCO Global Geopark, Portugal)" (PDF). Geoheritage. 9 (4): 3. doi:10.1007/s12371-016-0203-2. hdl:1822/45592. S2CID 132477543.
  32. ^ Cheshire, S. G.; Bell, J.D. (1 December 1976). "The Speedwell Vent, Castleton, Derbyshire: A Carboniferous Littoral Cone". Proceedings of the Yorkshire Geological Society. 41 (2): 173–184. Bibcode:1976PYGS...41..173C. doi:10.1144/pygs.41.2.173.
  33. ^ "PLIOCENE/PLEISTOCENE BASALTIC PILLOW LAVA AND TUFF ALONG NW SHORE OF LAKE TAHOE, CA: NEARSHORE VENT OR LITTORAL CONE?". gsa.confex.com. Retrieved 2016-11-24.
  34. ^ Huber, M. S.; Byerly, G. R. (1 December 2018). "Volcanological and petrogenetic characteristics of komatiites of the 3.3 Ga Saw Mill Complex, Weltevreden Formation, Barberton Greenstone Belt, South Africa". South African Journal of Geology. 121 (4): 479. Bibcode:2018SAJG..121..463H. doi:10.25131/sajg.121.0031. ISSN 1012-0750. S2CID 56281060.

Sources

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